1. Field of the Invention
The present invention relates to an exposure apparatus which is used to expose a fine pattern in a manufacturing process of a semiconductor integrated circuit, etc., and more particularly to an electron beam proximity exposure apparatus in which a mask having an aperture corresponding to a pattern to be exposed is disposed in proximity to a surface of an object such as a semiconductor wafer and the mask is irradiated with an electron beam, thereby performing exposure of the pattern to an electron beam having passed through the aperture.
2. Description of Related Art
Attempts are being made to enhance integration degrees of semiconductor integrated circuits and finer circuit patterns are desired. Presently, a limit of the finer circuit patterns is defined mainly by exposure apparatuses, and a stepper which is an optical exposure apparatus takes various measures such as a light source which emits rays having shorter wavelengths, a larger NA (numerical aperture) and a phase shift method. However, much finer circuit patterns involve various kinds of problems such as a rapid increase of a manufacturing cost. New types of exposure apparatus such as an electron beam direct lithography apparatus and X-ray exposure apparatus have therefore been developed, but there still remain many problems in terms of stability, productivity, cost and so on.
An electron beam proximity exposure system is conventionally under research and development, since the exposure principle thereof is simple, as xe2x80x9cHigh Throughput Submicron Lithography with Electron Beam Proximity Printingxe2x80x9d (H. Bohlen et al., Solid State Technology, September 1984, pp. 210-217) (hereinafter referred to as literature 1) exemplifies. However, it was thought that it was of no practical use since it was difficult to eliminate the proximity effect peculiar to the electron beam.
U.S. Pat. No. 5,831,272 (corresponding to Japanese Patent No. 2951947) and xe2x80x9cLow energy electron-beam proximity projection lithography: Discovery of missing linkxe2x80x9d (Takao Utsumi, J. Vac. Sci. Technol. B 17(6), November/December 1999, pp. 2897-2902) disclose an electron beam proximity exposure apparatus that overcomes the above-mentioned problems and is usable for processing with very fine resolution at a mass production level.
FIG. 1 is a diagram showing a fundamental configuration to realize the electron beam proximity exposure apparatus disclosed by U.S. Pat. No. 5,831,272. In an electron optical column 10 are disposed an electron gun 14 which emits electron beam 15, a condenser lens 18 which collimates the electron beam 15, a main deflecting coil 20 and a subsidiary deflecting coil 50 as shown in FIG. 1. Though the main deflecting coil 20 is shown as a single deflecting coil in FIG. 1, they actually are configured in two stages so as to obtain electron beams which are in parallel with an optical axis and have different irradiating locations by deflecting an electron beam with a deflecting coil in a first stage and then in a reverse amount with a deflecting coil in a second stage. Similarly, the subsidiary deflecting coil 50 is also configured actually in two stages so that fine adjustment of an irradiating angle is possible without changing the irradiating locations changed with the main deflecting coils by deflecting the electron beams with a deflecting coil in a first stage and then in a reverse amount twice as large with a deflecting coil in a second stage. In a vacuum object chamber 8 are disposed a mask stage 36 which holds and moves a mask 30, a reflected electron detector 38 which detects reflected electrons, a wafer stage 44 which holds and moves a wafer 40, a standard mark 60 disposed on the wafer stage 44, and a height detector 46 which detects height of the wafer 40. Furthermore, a laser length measuring device 38 for the mask stage which detects travel amount of the mask stage 36 and a laser length measuring device 48 for the wafer stage which detects travel amount of the wafer stage 44 are disposed so that the travel amounts of the stages can be detected with remarkably high accuracy. The wafer stage 44 is movable in directions of at least two axes. Though the reflected electron detector 38 is used in this configuration, a secondary electron detector can also be used in place of this detector which detects secondary electrons.
The electron beam proximity exposure apparatus is controlled by a computer 70. Signals detected by the laser length measuring device 38 for the mask stage and the laser length measuring device 48 for the wafer stage are supplied to a data bus of the computer 70. Signals detected by the reflected electron detector 38, a detector disposed on the standard mark and the height detector 46 are supplied to a signal processor circuit 76, converted into digital signals and then supplied to the data bus of the computer 70. The condenser lens 18 is an electromagnetic lens or an electrostatic lens which is controlled by the computer 70 by way of a condenser lens power source 71. The computer 70 supplies deflection amount data to a digital arithmetic circuit 75, which performs an operation to correct the deflection amount data according to previously stored correction data and supplies corrected data to a main DAC/AMP 73 and a subsidiary DAC/AMP 74. The main DAC/AMP 73 and the subsidiary DAC/AMP 74 convert the corrected deflection amount data into analog signals, amplify the analog signals and supply the resulting signals to the main deflecting coil 20 and the subsidiary deflecting coil 50. The electron beam is deflected as desired accordingly.
The exposure apparatus described above positions the wafer 40 to the mask and exposes a pattern over an entire surface of the mask by scanning the electron beam 15.
In case of a photomask to be used in a optical light exposure apparatus such as a stepper, a chromium layer or the like is patterned on a glass substrate, the glass substrate is checked whether or not the pattern is formed as predetermined and a pellicle layer is formed as a protective film on the pattern immediately when the pattern is free from a defect or after correcting a defect with a correcting device if any. A surface of the pellicle layer is monitored for dust adhesion and is cleaned when dust adheres on a problematic level. The pattern is not injured by cleaning. The surface of the pellicle layer causes defocusing by its thickness and no particular problem occurs so far as the adhering dust consists of small particles.
In contrast, a mask 30 which is to be used in the above described electron beam proximity exposure apparatus needs to be a stencil mask having an aperture formed as a hole on which the above described pellicle layer cannot be formed. Accordingly, dust or the like adhering to a surface of the mask causes a serious problem in the above described electron beam proximity exposure apparatus. This mask for proximity exposure is set in the electron beam exposure apparatus after being manufactured with a separate apparatus and inspected, but it is impossible to completely prevent dust from adhering to the surface of the mask for proximity exposure while it is carried from an inspecting device to the electron beam exposure apparatus. Accordingly, there arises a problem that even a mask which is free from a defect at an inspection stage cannot be warranted to be free from a defect when it is set in the electron beam exposure apparatus.
When a defect is produced by dust which adheres during use in the electron beam proximity exposure apparatus in particular, the surface of the mask can hardly be cleaned directly and a defective portion will be corrected with an apparatus such as a correcting device. When the mask for proximity exposure is removed from the electron beam proximity exposure apparatus, carried to an inspecting device and the correcting device or a cleaning device and set once again in the electron beam proximity exposure apparatus after correction or cleaning is completed, however, it is impossible to completely prevent dust from adhering to the surface of the mask for proximity exposure as described above. Thus, it is impossible for the above described electron beam proximity exposure apparatus to assure that a mask for proximity exposure is free from a defect which is set in the exposure apparatus.
Furthermore, a mask 30 which is to be used in the above described electron beam proximity exposure apparatus is a stencil mask having an aperture formed as a hole. An annular pattern which has a small circular square pattern 342 in a large square pattern 341 and an aperture as a portion 343 between the large and small square patterns, for example as shown in FIG. 2(a), cannot be exposed with a single mask, and it is necessary to divide this annular pattern into a pattern 344, 345 as shown in FIGS. 2(b) and 2(c) and a pattern 346, 347, and expose these patterns in two stages. In other words, it is necessary to prepare two masks for proximity exposure, expose the pattern with one of the masks set in the electron beam proximity exposure apparatus and then expose the pattern with the other mask set in the electron beam proximity exposure apparatus. In this case, however, it is necessary after first exposure to take a wafer out of a vacuum chamber into an atmospheric environment and carry the wafer again into the vacuum chamber of the electron beam proximity exposure apparatus for second exposure. In other words, it is necessary to carry the wafer repeatedly between a vacuum condition and the atmospheric condition. Accordingly, there arises not only a problem of lowered a throughput but also a problem to allow dust or the like to easily adhere, thereby lowering a yield.
A first object of the present invention is to solve such a problem or to make it possible to dispose a mask for proximity exposure which is free from a defect in an electron beam proximity exposure apparatus.
A second object of the present invention is to solve such a problem or to realize an electron beam proximity exposure apparatus which provides high throughput and high yield.
To accomplish the above described first object, an electron beam proximity exposure apparatus according to a first aspect of the present invention comprises a mask inspecting device, a mask correcting device, a mask cleaning device or a combination of these devices and a mask carrying path which allows to carry a mask in a vacuum condition among these devices.
More particularly, the electron beam proximity exposure apparatus according to the present invention comprises an electron beam proximity exposure section which exposes a pattern corresponding to an aperture of a mask on a surface of an object with an electron beam having passed through the aperture of the mask disposed in proximity to the surface of the object, and/or a mask inspecting section which inspects the mask and/or a mask correcting section which corrects the mask and/or a mask cleaning section which cleans the mask and a mask carrying mechanism which carries the mask between the electron beam proximity exposure section and the mask correcting section and/or the mask cleaning section, and is characterized in that the electron beam proximity exposure section, and/or the mask inspecting section and/or the mask inspecting section and/or the mask correcting section and/or the mask cleaning section and the mask carrying mechanism are communicated with one another through a common vacuum path so that a mask can be carried in a vacuum condition among these members.
Since it may be necessary to introduce a gas into a vacuum chamber through the mask correcting section and/or the mask cleaning section, it is desirable that the electron beam proximity exposure apparatus further comprises a mask correcting section shielding mechanism and/or a mask cleaning section shielding mechanism which shield interiors of the mask correcting section and/or the mask cleaning section from other sections.
The electron beam proximity exposure apparatus according to the first aspect of the present invention remarkably lowers a possibility of adhesion of dust and the like in the course of carriage since the mask carrying mechanism is capable of disposing a mask inspected with the mask inspecting section, a mask corrected with the mask correcting section and a mask cleaned with the mask cleaning section at a predetermined location in the electron beam proximity exposure section through the common vacuum path in no contact with external air.
In order to accomplish the above described secondary object of the present invention, an electron beam proximity exposure apparatus in a second mode of the present invention comprises two electron beam proximity exposure sections in a vacuum chamber to expose a pattern twice with two masks or a mask switching mechanism which is capable of switching either of two masks in an electron beam proximity exposure section.
Speaking more concretely, the electron beam proximity exposure apparatus according to the second aspect of the present invention is an electron beam proximity exposure apparatus which exposes a pattern corresponding to an aperture of a mask on a surface of an object with an electron beam that has passed through the aperture of the mask disposed in proximity of the surface of the object, in which the pattern is exposed twice first with a first mask and then with a second mask. Furthermore, the exposure apparatus comprises a first electron beam proximity exposure section comprising a first electron beam source which emits a first electron beam, a first mask which is disposed in a path of the first electron beam and a first stage which holds and moves the object, a second electron beam proximity exposure section comprising a second electron beam source which emits a second electron beam, a second mask which is disposed in a path of the second electron beam and a second stage which holds and moves the object, and an object carrying mechanism which carries the object exposed in the first electron beam proximity exposure section to the second electron beam proximity exposure section, the first electron beam proximity exposure section, the second electron beam proximity exposure section and the object carrying mechanism communicating with one another through a common vacuum chamber.
Furthermore, another electron beam proximity exposure apparatus according to the second aspect of the present invention is an electron beam proximity exposure apparatus comprising a source of an electron beam which emits an electron beam, a mask which is disposed in a path of the electron beam and a stage which holds and moves an object and configured to expose a pattern corresponding to an aperture of a mask on a surface of an object with an electron beam having passed through the aperture of the mask disposed in proximity of the surface of the object, characterized in that the pattern is exposed twice with a first mask and a second mask and that the exposure apparatus comprises a mask switching mechanism which selects either of the first mask or the second mask to be used.
It is desirable that a mask inspecting device, a mask correcting device and a mask cleaning device are integrated with one another in the electron beam proximity exposure apparatus according to the second aspect like that according to the first aspect.
The electron beam proximity exposure apparatus according to the second aspect of the present invention is capable of performing the exposure successively with the first and second masks while maintaining an object in the vacuum chamber, thereby enhancing a throughput and a yield by reducing adhesion of dust and the like.